1. Field of the Invention
The present invention relates to a radiation generating apparatus including a movable diaphragm unit including a light projecting and sighting system (hereinafter, referred to as “light projecting/sighting system”) for making a simulation display of a radiation field as a visible light field, and to a radiation imaging system using the radiation generating apparatus.
2. Description of the Related Art
A typical radiation generating apparatus includes a radiation generating unit including a radiation tube and a movable diaphragm unit provided on a front surface of a radiation transmission window of the radiation generating unit.
As disclosed in Japanese Patent Application Laid-Open No. H07-148159, the movable diaphragm unit includes a light projecting/sighting system including a reflecting plate that transmits radiation and reflects visible light and a light source of visible light. The movable diaphragm unit further includes limiting leaves for defining a radiation field and a visible light field formed correspondingly thereto. The light source is provided off an irradiation path of radiation which irradiates a necessary radiation field so as not to interfere with the radiation when emitted. The reflecting plate is provided so as to be slanted with respect to a central axis of the radiation in order to reflect visible light from the light source provided in this way to form a visible light field for making a simulation display of the radiation field. Further, the light source and the reflecting plate are, together with the limiting leaves, provided in an envelope which blocks radiation. The envelope is formed of a material which can attenuate radiation that impinges on the reflecting plate and the limiting leaves to be dispersed.
However, in the conventional movable diaphragm unit, the reflecting plate of the light projecting/sighting system is provided so as to be slanted, and thus, the envelope covering the reflecting plate becomes large, which is a factor in hindering size reduction of the radiation generating apparatus and a radiation imaging system using the radiation generating apparatus. Further, the material for forming the envelope which can attenuate radiation is a heavy mass material, and thus, there is a problem of increased weight.
On the other hand, the conventional movable diaphragm unit has an advantage in that, when the radiation tube provided in the radiation generating apparatus is a reflection type radiation tube, the reflecting plate provided so as to be slanted can alleviate, by the heel effect, the radiation quantity and radiation quality distribution. However, when a radiation tube of a transmission type which does not cause the heel effect is used, the reflecting plate provided so as to be slanted generates the radiation quantity and radiation quality distribution.